1. Field of the Invention
This invention relates to a lifting mechanism, more particularly, a lifting mechanism having a closed position of low height and having an increasing lifting power upon extension upwardly.
2. Problems in the Art
Many different lifting mechanisms have been developed and are currently used. Because of the diverse requirements needed for various lifting tasks, a variety of lifting principals as well as a variety of different structures exist with regard to these lifting mechanisms.
A common lifting mechanism is a pivotally connected cross lever jack commonly known as a scissors jack. Examples of such a jack and its operation can be seen in the U.S. Pat. Nos. 2,508,934 to Berg, 2,567,681 to Schwartz et. al., and 3,997,143 to Rose. Some of the reasons for the widely adopted success of the scissors-type jack are its simplicity in structure, its relatively small weight compared to its strength and durability, its small size compared to its lifting power, and its compact size compared to its lifting height.
A usual means for causing the scissor-type jack to raise and lower is the utilization of a screw rod which is threaded through block members pivotally attached to opposing pairs of scissored arms. An improvement to the scissors-jack consisted of utilizing hydraulic power to a cylinder to replace the screw rod and blocks. Further improvements consisted of utilizing electric power in conjunction with the screw rod and blocks.
Although the advantages of the scissors-type jack have been pointed out, problems and difficiencies still exist with this type of device. Because of the crossed nature of its lifting links, the scissors-type jack cannot be compressed to a minimum height, or extended to maximum height to the extent that is needed or desired at times. The lifting power of such a jack is many times insufficient over the entire lifting range. Stability also becomes a problem, particularly at more extended positions. The structure of the scissors jack also does not allow for drive means such as hydraulic cylinders or electronic motors to be placed in the middle of the jack, but rather must be positioned outside thereby unbalancing the jack and contributing to some instability.
It is therefore a primary object of the invention to provide a lifting mechanism which solves or improves over the deficiencies in the art.
A further object of this invention is to provide a lifting mechanism which can attain a small collapsed minimum height.
A further object of this invention is to provide a lifting mechanism which can also be extended to a high maximum height.
Another object of this invention is to provide a lifting mechanism which exerts increased lifting power as it is extended upwardly.
Another object of the invention is to provide a lifting mechanism which is simple in structure and operation.
A further object of this invention is to provide a lifting mechanism which has stability and strength.
Another object of the invention is to provide a lifting mechanism which can be adapted to operate in conjunction with a variety of power mechanisms.
Another object of the invention is to provide a lifting mechanism which is durable, economical, and easy to transport and maintain.
These and other objects, features, and advantages of the invention will become aparent with reference to the accompanying specification and claim.